Method for Recirculating a Partial Exhaust Gas Flow to an Internal Combustion Engine of a Motor Vehicle

ABSTRACT

In the present method, a partial flow is guided through a partial flow line connected downstream of an exhaust gas outlet of an internal combustion engine, and is immediately thereafter supplied to an internal combustion engine either via a first valve, a bypass line which is connected directly downstream and a recirculation line. Alternatively, the partial exhaust gas flow can be supplied to the internal combustion engine via a second valve, a radiator which is connected directly downstream and a recirculation line. The first valve and the second valve are opened or closed as a function of the exhaust gas conditions, this being monitored by a sensor. A device for carrying out the method is also disclosed.

The invention relates to a method for recirculating a partial exhaustgas flow to an internal combustion engine of a motor vehicle. Theinvention also relates to a device for carrying out the method.

Methods for recirculating partial exhaust gas flows to an internalcombustion engine are known. DE-Patent 196 80 305 C2 describes anexhaust gas recirculation system for an internal combustion engine. Inthis system, some of the exhaust gases produced by the engine arerecirculated from an exhaust line of the engine into an intake line ofthe engine, the exhaust gas recirculation system having a recirculationline downstream of the exhaust line of the engine. This recirculationline splits into a bypass line and a radiator line having an integratedradiator. The bypass line and the radiator line each have a valve attheir end, downstream of which the bypass line and the radiator line areonce again combined into a single line. The partial exhaust gas flowthen flows back into the engine via this line. A disadvantage of thismethod is however that the two valves become clogged relatively quicklyby particulates and condensate products in the exhaust gas, whichaffects both the actual operation and the actuation of the two valveswhich are completely opened or completely closed alternately to oneanother. The valves are actuated by an electronic control unit such thatthe partial exhaust gas flow flows via the bypass line in operatingmodes at low engine temperature or low engine load, and via the radiatorline in other engine operating modes. The clogging of the valves has anadverse effect on the actuation by the electronic control unit so thatvarying exhaust gas conditions can only be reacted to with a time lag.It is therefore the object of the invention to provide a method forrecirculating a partial exhaust gas flow to an internal combustionengine of a motor vehicle in which clogging of shut-off valves islargely prevented. It is also the object of the invention to produce adevice for carrying out the method.

The object on which the invention is based is achieved by means of amethod for recirculating a partial exhaust gas flow to an internalcombustion engine of a motor vehicle, in which the partial flow isguided through a partial flow line connected downstream of the exhaustgas outlet of the internal combustion engine, and is immediatelythereafter supplied to the internal combustion engine either via a firstvalve, a bypass line which is connected directly downstream and arecirculation line or via a second valve, a radiator which is connecteddirectly downstream and a recirculation line, the first and secondvalves being opened or closed as a function of the exhaust gasconditions, this being monitored by a sensor. Both the first valve andthe second valve are connected in parallel between the partial flow lineand the bypass line or radiator respectively. They are cooled duringoperation. The operating modes of the first valve and second valve,which are to be set as a function of the exhaust gas conditions, aremonitored by the sensor. In this case, intermediate positions arepossible so that two functions are to be assigned to the first valve andthe second valve. On the one hand, these are used to control whether thepartial flow is guided through the bypass line or through the radiator.On the other hand, these are used to set the size or volume of thepartial flow.

Surprisingly, it has been shown in the method that deposits in the firstvalve and in the second valve are avoided after relatively short periodsof operation. The exhaust gases which are guided through the first valveor through the second valve remain at a temperature which is such thatno caking occurs in the first valve or in the second valve. Nodisadvantageous condensate products accumulate either in the first valveor in the second valve, since the bypass line and the radiator areconnected downstream of the first valve and the second valverespectively. It is also advantageous that both the first valve and thesecond valve can be actuated for relatively long periods of operationwith virtually no time lag, so that varying exhaust gas conditions canbe reacted to relatively quickly.

In one preferred embodiment of the invention, the partial flow is guidedthrough a valve unit which comprises the first valve, the second valveand the sensor. By integrating the first valve, the second valve and thesensor to form a valve unit, the installation space is reduced, as isgenerally desirable in motor vehicles. In addition, the use of a valveunit is advantageous in that it can be pre-manufactured, which isfavourable for the production process.

According to a further embodiment of the invention, the partial flowdownstream of the second valve is guided through a radiator, arranged asthe radiator which is connected downstream, having liquid coolant, theliquid coolant being guided both through the radiator which is connecteddownstream and through the valve unit. A water mixture is generally usedas the liquid coolant. In this case, it is generally advantageous if thevalve unit and the radiator which is connected downstream have a commonhousing through which the liquid coolant is guided by means of forexample radiator coils. In this way, installation space isadvantageously saved and cooling performance optimized.

The object on which the invention is based is also achieved by means ofa device for carrying out the method, which comprises a partial flowline which is connected to a first valve and to a second valve, thefirst valve being connected to a recirculation line by means of a bypassline and the second valve being connected to a recirculation line bymeans of a radiator which is connected directly downstream, and a sensorbeing arranged which monitors both the actuation of the first valve andof the second valve as a function of the exhaust gas conditions. Bymeans of the respective arrangement of the first valve and of the secondvalve upstream of the bypass line and upstream of the radiator which isconnected directly downstream, accumulations in the first valve and inthe second valve can be advantageously avoided in such a way thatrelatively fast actuation is ensured even with varying exhaust gasconditions.

According to a further advantageous embodiment of the invention, it isprovided that a radiator having liquid coolant is arranged as theradiator which is connected downstream. In this way, the temperature ofthe exhaust gases can be reduced relatively quickly.

In a further embodiment of the invention, a valve unit is arranged whichcomprises the first valve, the second valve and the sensor. In thiscase, this is a structural subunit, the arrangement of whichadvantageously reduces the installation space required.

According to a further embodiment of the invention, the radiator whichis connected downstream comprises a coolant inlet and the valve unitcomprises a coolant outlet. This means that the same coolant flowsthrough and thus cools both the radiator which is connected downstreamand the valve unit, which is likewise advantageous in terms of reducingthe size of the installation space. The coolant inlet and the coolantoutlet can advantageously be formed for example in the form of pipeconnecting pieces.

The invention is explained in the following in more detail and by way ofexample on the basis of the drawing (FIGURE).

FIGURE shows a method flow chart of the method for recirculating apartial exhaust gas flow to an internal combustion engine of a motorvehicle.

FIGURE illustrates a method flow chart of the method for recirculating apartial exhaust gas flow to an internal combustion engine 1 of a motorvehicle. The exhaust gas flows out of the internal combustion engine 1into the partial flow line 2 via the exhaust gas outlet la. Only thepartial exhaust gas flow is then guided in the partial flow line 2. Theremaining volume of exhaust gas flows via the exhaust line 14 to theexhaust (not illustrated). Immediately downstream of the partial flowline 2, the partial exhaust gas flow is supplied back to the internalcombustion engine 1 either via a first valve 3, a bypass line 5 which isconnected directly downstream and a recirculation line 7 or via a secondvalve 4, a radiator 6 which is connected directly downstream and arecirculation line 7. The exhaust gas conditions determine whether thepartial exhaust gas flow is guided via the first valve 3 and the bypassline 5 or via the second valve 4 and the radiator 6 which is connecteddirectly downstream. These respective procedures are monitored by meansof a sensor 8. This means that either the first valve 3 or the secondvalve 4 is opened or closed depending on the exhaust gas conditions. Atlow exhaust gas temperatures or at low engine power, the partial flow isguided via the bypass line 5, and at higher temperatures or at highengine power, via the radiator 6 which is connected directly downstream.The recirculation line 7 issues directly into a gas inlet line 1 b whichis directly connected to the internal combustion engine 1. Air is alsoadded via a supply line 12 into the gas inlet line 1 b, so that amixture of the partial exhaust gas flow and air flows into the internalcombustion engine 1 via the gas inlet line 1 b. The radiator 6 which isconnected directly downstream is embodied as a radiator having liquidcoolant. It has a coolant inlet 10 through which the coolant flows intothe radiator 6 which is connected downstream. The liquid coolant thenflows via the radiator 6 which is connected directly downstream into thevalve unit 9 which comprises the first valve 3, the second valve 4 andthe sensor 8. The valve unit 9 has a coolant outlet 11 through which theliquid coolant is discharged from the system. The first valve 3 and thesecond valve 4 are operated by an electric motor 12 which is likewisearranged in the valve unit 9. The fuel for the internal combustionengine 1 is supplied to the internal combustion engine 1 via the fuelline 13.

1. A method for recirculation a partial exhaust gas flow to an internalcombustion engine of a motor vehicle, comprising the steps of: guidingthe partial flow through a partial flow line connected downstream ofexhaust gas outlet of the internal combustion engine, supplying thepartial flow immediately thereafter to the internal combustion engineeither via a first valve, a bypass line which is connected directlydownstream and a recirculation line or via a second valve, a radiatorwhich is connected directly downstream and a recirculation line, openingor closing the first valve and the second valve as a function of theexhaust gas conditions, and monitoring the opening and closing with asensor.
 2. The method according to claim 1, wherein the partial flow isguided through a valve unit which comprises the first valve, the secondvalve and the sensor.
 3. The method according to claim 2, wherein thepartial flow downstream of the second valve is guided through aradiator, arranged as the radiator which is connected downstream, havingliquid coolant, the liquid coolant being guided both through theradiator which is connected downstream and through the valve unit.
 4. Adevice for recirculating a partial exhaust gas flow to an internalcombustion engine of a motor vehicle, comprising: a partial flow line; afirst and second valve connected to the partial flow line; arecirculation valve connected to the first valve by means of a bypassline; a radiator arranged to connect the second valve directlydownstream to the recirculation line; and a sensor arranged to monitorsactuation of the first valve and of the second valve as a function ofthe exhaust gas conditions.
 5. The device according to claim 4, whereinthe radiator includes liquid coolant and is arranged downstream.
 6. Thedevice according to claim 5, further comprising a valve unit includingthe first valve, the second valve and the sensor.
 7. The deviceaccording to claim 6, wherein the radiator is connected downstream andcomprises a coolant inlet and the valve unit comprises a coolant outlet.